Proposed patch for renaming constraints along with indexes

As per my suggestion just now for resolving bug #3854.

I'm thinking in terms of applying this for 8.3, but not back-patching
--- though I suppose depending on how seriously you take the bug, a case
could be made for back-patching.

I don't offhand see anyplace that this would need to be documented,
except as a release-note item.

Comments?

regards, tom lane